Systems for measuring velocities of moving bodies

ABSTRACT

In the system disclosed a random noise signal frequencymodulates a Doppler radar. More specifically the relative velocity between moving bodies or between a moving body and a fixed object is measured by transmitting an undulatory signal toward the body and receiving the reflected wave whose frequency has been shifted by the Doppler effect. The Doppler signal is detected by a homodyne detection system using a portion of the transmission signal as a reference. The transmitted undulatory signal exhibits frequency-modulation generated by a random noise signal. A portion of the frequency modulated undulatory wave is used as a reference. The frequency modulation by the random noise prevents erroneous operation caused by interference between different transmitted undulatory signals.

Unite Sato et al.

tes ate 1451 Sept. 4, 1973 SYSTEMS FOR MEASURING VELOCITIES OF MOVINGBODIES [73] Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Tokyo,Japan 22 Filed: Mar. 1, 1971 21 Appl.,No.: 119,465

RANDOM NOISE SIG GE N BAND-PASS F LT Primary ExaminerT. H. TubbesingAttorney-Toren & McGeady [57] ABSTRACT In the system disclosed a randomnoise signal frequency-modulates a Doppler radar. More specifically therelative velocity between moving bodies or between a moving body and afixed object is measured by transmitting an undulatory signal toward thebody and receiving the reflected wave whose frequency has been shiftedby the Doppler effect. The Doppler signal is detected by a homodynedetection system using a portion of the transmission signal as areference. The transmitted undulatory signal exhibitsfrequency-modulation generated by a random noise signal. A portion ofthe frequency modulated undulatory wave is used as a reference. Thefrequency modulation by the random noise prevents erroneous operationcaused by interference between different transmitted undulatory signals.3

10 Claims, 3 Drawing Figures PATENTED 3.757. 329

4 FIG. a Q

i RANDOM NOISE BAND PASS F R E Q ICIRCULATOR s G GEN F LT M 00 2 3HOMODYNE DET LOW-PASS 8 F LT L 9- DISPLAY KAZUO SANFIZJENTORS HlSASHIWATAMABE Tmem amo lfifi a? ATTORNE 5 SYSTEMS FOR MEASURING VELOCITIES FMOVING BODIES BACKGROUND OF THE INVENTION This invention relates tosystems for measuring the velocities of moving bodies, particularlywhere the relative velocity between moving bodies or between a movingbody and a fixed object is measured by means of the Doppler effect uponundulatory signals. The invention has special, although not exclusive,relevence to systerms which measure the relative velocities of vehiclessuch as automobiles, to sense impending collisions.

It is generally known that when undulatory energy such as sound waves,electromagnetic waves, or the like, is radiated from one position andencounters an object having a velocity component toward or away from thesource, the frequency of the wave reflected from the object is shiftedwith respect to the frequency of the transmitted wave. This is known asthe Doppler effect. It is used in so-called Doppler radars.

If the frequency of a wave transmitted from one object is f,; thevelocity of propagation of undulator energy c; and the relative velocitybetween a transmission source and a body, either toward or away from thesource, v; then the frequency f, of the received wave will be defined asThe frequency f,, of the Doppler signal, which represents the differencebetween f, and f, that results from the Doppler effect has the value Thevelocity v is measured directly by setting the frequencyfl of thetransmission wave, and the propagation velocity 0, so that theyrepresent constant values.

Velocity measuring systems using this Doppler principle may, forexample, be composed of a high frequency energy generator, a circulatorhaving an antenna, a homodyne detector and a low pass filter. In such asystem the circulator successively radiates a constant-frequencytransmission wave produced by the generator, through the antenna, towardan oncoming or receding object. At the same time, the circulatorreceives the wave reflected from the oncoming object. The frequency ofthe reflected wave is shifted by the Doppler effect. The homodynedetector utilizes a reference signal, that is a local oscillator signal,formed from part of the energy of the transmission wave extracted fromthe circulator. The homodyne produces a Doppler signal having afrequency proportional to the relative velocity, by mixing and detectingthe reference signal and the received wave. Consequently, in thehomodyne detection system as described above, a significant Dopplersignal is detected only where a transmission wave is formed as anintrinsic function of the system.

However, frequencies of transmission signals usable in such measuringsystems are limited by their characteristics. Thus the frequency bandsusable are inevitably limited. If these frequencies are used as acollision sensing apparatus in vehicles such as automobiles, and suchmeans are mounted on a vast number of vehicles, it is possible thattransmission waves from several vehicles may overlap. Thus, twotransmission waves from vehicles may interfere with each other and thefrequency difference between two transmitted waves may become equal tothe frequency of the Doppler signal to be detected. Then a Dopplersignal may result, as if two vehicles were moving toward each other,even when there is no actual motion. This results in undesirableerroneous operation.

An object of the invention is to improve systems, such as Dopplerradars, of this type.

Another object of this invention is to eliminate the above describederroneous operation caused by interference of transmission waves.

Still another object of the invention is to accomplish this simplywithout complex equipment.

SUMMARY OF THE INVENTION According to a feature of the invention thesedeficiencies of prior systems are obviated, and the objects obtained, byfrequency-modulating the transmission wave irregularly with a randomnoise signal and detecting the Doppler signal by using a portion of theenergy from the transmission wave as a reference signal.

By virtue of this feature the likelihood of interference between wavestransmitted by several sources may be reduced.

According to another feature of the invention the modulation frequencyand modulation index of the transmitting signal are determined inaccordance with the frequency components of the random signal.

According to still another feature of the invention limiting means limitthe frequency range of the modulation of the transmitted signal.

According to still another feature of the invention this limitingfunction is accomplished by a band pass filter.

According to still another feature of the invention low-pass filtermeans limit the frequency excursion of the Doppler signal.

These and other features of the invention are pointed out in the claims.Other objects and advantages of the invention will become obvious fromthe following detailed description when read in light of theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram illustratinga system embodying features of the invention;

FIG. 2a is a frequency-time wave form diagram illustrating the changesin the transmitted frequencies of two systems embodying features of theinvention; and

FIG. 2b is a frequency-time diagram illustrating an enlarged form of aportion of FIG. 20.

DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1, a random noise signalgenerator 1 produces random wave fonns whose frequency spectrum islimited by a band pass filter 2. A frequencymodulator 3 modulates theoutput frequency generated by an oscillator 4 in accordance with theband-passfilter modified random noise signals from the generator 1, andapplies the thus frequency-modulated signal to a circulator S. Thecharacteristics of the filter 2 establish the modulation frequency bandand the magnitude of the frequency deviation. A circulator 5 applies thethus frequency-modulated transmission signal to an antenna 6. The latterradiates the signal in the form of a transmission wave toward anoncoming object along a predetermined direction. The frequency shiftedwave reflected from the oncoming object is received by the antenna.

Circulators, such as the circulator 5, are discussed in the McGraw HillEncyclopedia of Science and Technology 1966 Edition, Volume 8, page 418as well as Volume 6 pages 302 to 305. Other types of duplexers andantenna systems may be substituted for the circulator and the antenna 6.

While the frequency-modulated wave is being transmitted and thefrequency shifted wave reflected, part of the frequency modulatedtransmission wave or transmission signal is utilized as a referencesignal in a homodyne detector 7. The latter forms a Doppler signal inresponse to the frequency-modulated transmission wave and the frequencyshifted wave in conventional manner.

As described above, the system according to this invention produces atransmission wave as well as a frequency deviated wave whose frequencieshave been modulated with the irregularity inherent in a random signal ata selected modulation index.

A low-pass filter 8 limits the frequency spectrum of the Doppler signalpassing from the homodyne detector 7 to a display 9. The low-pass filterin effect limits the frequency shifts displayed by the display 9 to amaximum frequency shift. The display 9 according to one embodiment ofthe invention constitutes a frequency counter. According to anotherembodiment of the invention the display 9 is a frequency-voltageconverter that displays the frequency in the form of a DC voltage value.

The system of FIG. 1 operates as follows. The modulation frequency(random noise signal frequency band) and the frequency shift of theoutput frequency generated by the oscillator 4 are selected in thefrequency modulator 3 by means of the output of the random noise signalgenerator 1. This frequency is modulated by setting a specific valueconforming to the height of the modulation frequency and the magnitudeof the frequency deviation according to the filter characteristics ofthe band-pass filter 2. The thus frequencymodulated transmission signalis applied by a circulator 5 to an antenna 6 which radiates the signalas a transmission wave form in a predtermined direction toward anoncoming object. The antenna receives a frequency shifted wave reflectedfrom the oncoming object. The circulator 5 applies the received signalto the homodyne detector 7. At the same time part of thefrequency-modulated transmission signal or wave is applied as areference signal to the homodyne detector in conventional manner. Thehomodyne detector mixes and converts the two frequencies into a beatfrequency, or Doppler signal. The frequency of the Doppler signal isapproximately proportional to the velocity component of the object inthe direction of the antenna. For an oncoming object or a recedingobject traveling radially with respect to the antenna the relativevelocity is proportional to the Doppler frequency.

The range of velocities represented by Doppler frequencies which areused in the display 9 is limited at an upper level by the low-passfilter 8. The display 9 may also constitute a utilization circuit. Thesystem of FIG. 1 is capable of obviating the effects of interferencebetween a reflected wave form and one or more other wave formstransmitted by other transmitters in the same frequency band. Receptionof such multiple signals may occur if several automobiles in onevicinity each possess a Doppler radar corresponding to the radar systemof FIG. 1 and each operates at overlapping frequency bands. Theapparatus of FIG. 1 even avoids problems occurring when there is noreflected signal and two transmitted signals in the same frequency bandare received from other antennae by the antenna 6.

FIG. 2a illustrates two transmitted wave formsf, and f, having the samecenter frequencyf which are irregularly varied with respective naturalrandom noise signals within the maximum frequency deviation 2Af,established by a modulation index. With such two signals there is apossibility that the frequency difference between the two wavesf, andfmay at times lie within the frequency range of Doppler signals detected,namely those passed by the low-pass filter 8, and cause interference.Such interference would normally occur as shown in FIG. 2b when thefrequency difference Af is measured near the coincidence points of thetwo transmission waves f and f However, because both transmission waves1",, and f, are randomly frequencymodulated, the time At during which anapparent Doppler signal is obtained in the Doppler signal frequency bandis comparatively small. The aspect of the change in the frequencydifference Af as well as the time A: during which interference continuesand the time intervals at which the interference is developed, namelythe frequency of occurrence, are controlled by the modulation frequencyand the frequency deviation. As a result the Doppler signal developed bythe interference is not sufficiently long and does not occur oftenenough to affect the display 9 significantly.

The modulation frequency and the frequency deviation selected by therandom noise signal are determined to produce an interference time Atthat constitutes a negligibly short time with respect to the variationsin the relative velocity to be detected. In other words, the modulationfrequency and frequency devia tion are selected to obtain a rapidfrequency change speed which cannot be produced by a moving body. Thusthe apparent Doppler signal developed by mutual interference is easilyseparated from the true Doppler signal detected only by the systems owntransmission wave.

The specific value determined by the band-pass filter characteristics isestablished so as to apply to such cases where interference occursfrequently due to the increase in modulation frequency band or where theinterference time At is shortened due to the increase in magnitude ofthe frequency deviation.

As described above, according to the system of this invention, it ispossible to convert a signal developed due to interference oftransmission waves to a signal that is substantially insignificant. Inthis case, the oscil lator may be substituted by Gunn effect oscillatorfor example.

The oscillator 4 used in the system of FIG. 1 may also serve as amodulator by superimposing the random signal directly on its biasvoltage. Therefore, according to another embodiment of the invention thefrequency modulator 3 is not required.

Also, there exists a time lag between the transmitted wave and thereceived wave. This is determined by the propagation velocity. Inutilizing the frequency modulated transmission wave as a referencesignal according to the system of FIG. 1, the frequency of the referencesignal changes during the propagation time lag. A beat wave due to thefrequency difference is developed between the transmitted wave and thereceived wave. Ac-

cording to another embodiment of the invention the modulation frequencyand modulation index is selected, on the basis of the range of distancesto be measured, to develop a beat frequency band due to the propagationtime lag which is distinct from the band of 5 frequencies of the Dopplersignal.

While embodiments of the invention have been described in detail it willbe obvious to those skilled in the art that the invention may bepracticed otherwise without departing from its spirit and scope.

What is claimed is:

l. A velocity measuring system, comprising energy generating means forcontinuously transmitting undulatory waves from one position andreceiving objectreflected undulatory waves at a position fixed relativeto the one position, frequency comparator means responsive to saidgenerating means for combining the frequency of the transmitted wavewith the frequency of the received wave to form a Doppler signal as ameasure of velocity, and exclusion means for identifying the transmittedundulatory waves so as to exclude velocity measurement with extraneoussignals, said exclusion means including modulating means forming a partof said generating means for continuously modulating the transmittedsignal on a random basis.

2. A system as in claim 1, wherein said modulating means includefrequency changing means for modulating the frequency of the transmittedsignal.

3. A system as in claim 2, wherein said modulating means includelimiting means for limiting the frequency range of the modulation of thetransmitted signal.

4. A system as in claim 1, wherein said modulating means include randomsignal generating means having band-pass filter means for controllingthe frequency output of said random generating means, and a modulatorresponsive to the output of said band-pass filter means.

5. A system as in claim 1, wherein said comparator means includeslow-pass filter means for limiting the frequency of the Doppler signal.

6. A system as in claim 5, wherein said generating means includeoscillator means for forming an altemating signal; wherein saidmodulating means includes random signal forming means for forming randomsignals, band-pass filter means for limiting the frequency range of therandom signals, and a modulator responsive to said band-pass filtermeans and connected to said generator means for modulating thetransmitted signal over a frequency range determined by said band-passfilter.

7. A velocity measuring system, comprising oscillator means forgenerating an undulating wave signal, frequency modulating meansresponsive to said oscillator means for randomly frequency-modulatingthe wave signal by a random noise signal which varies betweenpredetermined frequencies, transmitting and receiving means coupled tosaid frequency modulating means for transmitting the frequency-modulatedwave signal toward an oncoming object and for receiving the wave signalreflected by said oncoming object so that the wave signal received is aDoppler shifted, and homodyne detecting means coupled to saidtransmitting and receiving means for mixing the part of the transmittedwave signal as a reference signal with the reflected wave signal anddetecting the frequency shift as a measure of the relative velocity ofthe oncoming object.

8. An apparatus as in claim 7, wherein said homodyne detecting meansincludes low pass filter means for limiting the frequency of the Dopplersignal.

9. A system as in claim 7, wherein said frequency modulating meansincludes noise generator means, and band-pass filter means coupled tosaid noise generator means for establishing the predeterminedfrequencies between which the noise Signal varies.

10. An apparatus as in claim 9, wherein said frequency modulating meansincludes a modulator responsive to said band-pass filter means.

1. A velocity measuring system, comprising energy generating means forcontinuously transmitting undulatory waves from one position andreceiving object-reflected undulatory waves at a position fixed relativeto the one position, frequency comparator means responsive to saidgenerating means for combining the frequency of the transmitted wavewith the frequency of the received wave to form a Doppler signal as ameasure of velocity, and exclusion means for identifying the transmittedundulatory waves so as to exclude velocity measurement with extrAneoussignals, said exclusion means including modulating means forming a partof said generating means for continuously modulating the transmittedsignal on a random basis.
 2. A system as in claim 1, wherein saidmodulating means include frequency changing means for modulating thefrequency of the transmitted signal.
 3. A system as in claim 2, whereinsaid modulating means include limiting means for limiting the frequencyrange of the modulation of the transmitted signal.
 4. A system as inclaim 1, wherein said modulating means include random signal generatingmeans having band-pass filter means for controlling the frequency outputof said random generating means, and a modulator responsive to theoutput of said band-pass filter means.
 5. A system as in claim 1,wherein said comparator means includes low-pass filter means forlimiting the frequency of the Doppler signal.
 6. A system as in claim 5,wherein said generating means include oscillator means for forming analternating signal; wherein said modulating means includes random signalforming means for forming random signals, band-pass filter means forlimiting the frequency range of the random signals, and a modulatorresponsive to said band-pass filter means and connected to saidgenerator means for modulating the transmitted signal over a frequencyrange determined by said band-pass filter.
 7. A velocity measuringsystem, comprising oscillator means for generating an undulating wavesignal, frequency modulating means responsive to said oscillator meansfor randomly frequency-modulating the wave signal by a random noisesignal which varies between predetermined frequencies, transmitting andreceiving means coupled to said frequency modulating means fortransmitting the frequency-modulated wave signal toward an oncomingobject and for receiving the wave signal reflected by said oncomingobject so that the wave signal received is a Doppler shifted, andhomodyne detecting means coupled to said transmitting and receivingmeans for mixing the part of the transmitted wave signal as a referencesignal with the reflected wave signal and detecting the frequency shiftas a measure of the relative velocity of the oncoming object.
 8. Anapparatus as in claim 7, wherein said homodyne detecting means includeslow pass filter means for limiting the frequency of the Doppler signal.9. A system as in claim 7, wherein said frequency modulating meansincludes noise generator means, and band-pass filter means coupled tosaid noise generator means for establishing the predeterminedfrequencies between which the noise signal varies.
 10. An apparatus asin claim 9, wherein said frequency modulating means includes a modulatorresponsive to said band-pass filter means.